1. Field of the Invention
This invention relates to a bleaching composition for use in processing silver halide color photographic light-sensitive materials. More particularly, it pertains to a bleaching composition which prevents generation of harmful gases like halogen gas from a bleaching solution containing a bleaching agent and a halide.
2. Description of the Prior Art
In photographic processing of silver halide color photographic light-sensitive materials, the light-sensitive material (the silver halide photographic emulsion may be previously fogged) is usually imagewise exposed, and developed in a developer containing an aromatic primary amine in the presence of a dye-forming coupler to obtain a color image, whereas the simultaneously produced silver deposit is re-halogenated in the bleaching step and removed by fixing or bleach-fixing.
It has heretofore been known to use as a bleaching agent, red prussiates (ferricyanates), dichromates, ferric salts, organic acid ferric complexes, persulfates, or the like, and, as a re-halogenating agent, water-soluble halogenides such as ammonium chloride, sodium bromide, or the like. Of the above-described bleaching agents, ferricyanates are good bleaching agents in that they provide a sufficiently high bleaching rate (oxidation rate) to fully oxidize the silver deposit within a practically acceptable time. However, a bleaching solution containing red prussiate as a bleaching agent undergoes photolysis and release cyanide ion which causes environmental pollution. As a consequence, the waste solution must be decontaminated. Also, a bleaching solution containing dichromate must be decontaminated, after bleaching, so as not to discharge dichromate ion harmful which is from the standpoint of maintaining a sanitary environment. Conventional compositions which require decontamination treatments impose a serious burden on their industrial application.
It has been known to use persulfates, inorganic ferric salts, organic acid ferric complexes, etc. as a bleaching solution so as to remove the drawbacks of red prussiates or dichromates. In the case of using such bleaching agents, there are the following defects: Some of the bleaching agents are not soluble in a weakly acidic or alkaline solution and, in addition, a sufficiently high bleaching rate is difficult to attain. Thus, in many cases, the pH of the bleaching solution must be adjusted to a low level to remarkably strengthen the oxidizing power, thus the bleaching rate is increased. Adjustment of the pH to a low level to strengthen the oxidizing power is also effective using the aforesaid dichromate but, considering the treatment of the waste solution, the adjustment is particularly effective using persulfates or ferric salts because the load is comparatively light. However, adjusting the pH of the bleaching solution containing persulfate, inorganic ferric salt or organic acid ferric complex to a low level results in reaction between the chloride or bromide used in the system as the re-halogenating agent and the oxidizing agent and generation of the chlorine or bromine, which is a serious problem in the working environment. Further, the production of chlorine or bromine is accompanied by corrosion of developing equipment. Therefore, practical application of the bleaching process using persulfates or ferric salts as a bleaching agent is extremely difficult unless the above-described defects are removed.
As the compounds capable of preventing the production of chlorine or bromine due to oxidation of the chloride or bromide in the bleaching solution, there have been proposed gelatin, various amino acids, aliphatic monocarboxylic acids, cobalt salts, etc. as described in Research Disclosure, 17556 (Nov., 1978). However, many of these compounds do not sufficiently preventing generation of chlorine or bromine, while those which exhibit excellent gas generation-preventing effect have the defect of giving off other malodors, corroding the processing equipment, poor stability, accelerating decomposition of the persulfate to shorten the effective life of bleaching solution and reduce the bleaching ability, or suffering a serious change in the pH of the bleaching solution, thus showing poor stability.